Unsymmetrical dialkyl thiazole sulfenamides

ABSTRACT

UNSYMMETRICAL DIALKYL THIAZOLE SULFENAMIDES OF THE FORMULA   T-S-N(-R1)-CH(-R2)-R3   WHEREIN T IS BENZOTHIAZOLYL OR SUBSTITUTED BENZOTHIAZOLYL, WHERE THE SUBSTIUTENTS ARE CHLORO, BROMO, FLUORO, IODO, NITRO OR LOWER ALKOXY, R1 IS TERTIARY-ALKYL OF 4-12 CARBON ATOMS, R2 AND R3 ARE ALKYL OF 1-8 CARBON ATOMS OR TOGETHER WITH THE CARBON ATOM TO WHICH THEY ARE ATTACHED FORM CYCLOALKYL OF 5-8 CARBON ATOMS ARE DELAYED-ACTION ACCELERATORS

United States Patent 3,658,828 UNSYMMETRICAL DIALKYL THIAZOLE SULFENAMIDES John Joseph DAmico, Akron, Ohio, assignor to Monsanto Company, St. Louis, M0.

N0 Drawing. Filed Nov. 19, 1969, Ser. No. 878,243 Int. Cl. C07d 91/44 US. Cl. 260306.6 A Claims ABSTRACT OF THE DISCLOSURE Unsymmetrical dialkyl thiazole sulfenamides of the formula wherein T is benzothiazolyl or substituted benzothiazolyl, where the substituents are chloro, bromo, fluoro, iodo, nitro or lower alkoxy, R is tertiary-alkyl of 4-12 carbon atoms, R and R are alkyl of 1-8 carbon atoms or together with the carbon atom to which they are attached form cycloalkyl of 5-8 carbon atoms are delayed-action accelerators.

This invention relates to new thiazole sulfenamides. More particularly, it relates to unsymmetrical thiazole sulfenamide accelerators having a tertiary-alkyl radical and a secondary-alkyl or cycloalkyl radical attached to the sulfenamide nitrogen.

BACKGROUND OF THE INVENTION The N,N-dialkyl thiazolesulfenamides were among the first thiazolesultenamide accelerators discovered but general commercial acceptance lagged behind that of monoalkyl and cycloalkyl analogues. Some of them are liquids whereas solids are preferred because of easier purification, longer shelf life and greater convenience in mixing with rubber. Thiazolesulfenamides possess delayed action, a property which is valuable because of the processing safety it imparts. One theory of delayed action relates increasing delayed action to increasing steric hindrance but increasing steric hindrance of dialkyl amines increases difficulty of forming the sulfenamide.

Processing safety is a property which has great economic importance because in its absence rubber stocks ofttimes partially vulcanize before they can be shaped into useful articles. Fortunately, when styrene butadiene copolymer rubber became a commercial reality the delayed action thiazolesulfenamide accelerators had already been discovered and were available for use. The higher temperatures generated in the processing of styrene butadiene copolyrne'r rubber intensified the prevulcanization of scorch problem. However, even higher processing temperatures came into use and more scorchy carbon blacks were introduced so that improved delayed-action accelerators have been continually needed.

SUMMARY OF THE INVENTION It has now been discovered that highly sterically hindered thiazolesulfenamides containing one tertiary-alkyl and one secondary-alkyl or cycloalkyl on the amide nitrogen t'orm in good yields from the corresponding highly sterically hindered secondary amines. In spite of the lack of symmetry, the products are stable solids at ordinary temperatures and possess special delayed-action accelerating properties. The compounds of this invention may be represented by the formula:

wherein T is benzothiazolyl or substituted benzothiazolyl, where the substituents are chloro, bromo, fluoro, iodo, nitro or lower alkoxy, R is tertiary-alkyl of 4-12 carbon atoms, R and R are alkyl of 1-8 carbon atoms or together with the carbon atom to which they are attached form cycloalkyl of 5-8 carbon atoms.

Examples of tertiary-alkyl radicals suitable for the practice of this invention are tertiary-butyl, tertiary-amyl, tertiary-hexyl, tertiary-octyl, tertiary-nonyl, tertiary-decyl and tertiary-dodecyl. A tertiary-alkyl radical has its first carbon atom linked to three other carbon atoms.

The aliphatic groups from which R and R, can be selected include alkyl groups containing from 1-8 carbon atoms having straight or branched chains, for ex ample, methyl, ethyl, propyl, isopropyl, butyl, secondarybutyl, amyl, hexyl and octyl. Cyclopentyl, cyclohexyl and cyclooctyl are examples of radicals when R and R together with the carbon to which they are attached form cycloalkyl.

Compounds of this invention may be produced by the oxidative condensation of the appropriate secondary amine with a thiazole mercaptan or disulfide. Amines used in the preparation of these compounds are known. For example, N-isopropyl-tertiary-butyl amine is reported in Angew. Chem. vol. 72, 1001. N-tertiary-butyl cyclohexyl amine is reported in J. Org. Chem. vol. 29, 2240. Other amines needed to practice the invention can be made by known methods.

DESCRIPTION OF PREFERRED EMBODIMENTS Example 1 The preparation of N-tert-butyl-N-isopropyl-2-benzothiazolesulfenamide is as follows: 341.6 milliliters of a sodium hypochlorite solution containing 0.75 mole (16.4 grams NaOCl/ ml.) of sodium hypochlorite is added dropwise at 45-50 C. over a period of one and one-half hours to a slurry containing 84.6 grams (0.5 mole) of 2- mercaptobenzothiazole and 86.4 grams (0.75 mole) N- tert-butyl-N-isopropyl amine in 500 milliliters of isopropyl alcohol. To this reaction mixture 100 milliliters of hot water is added which results in formation of two liquid layers. This mixture is cooled to 30 C. and then added in one portion to 3000 grams of ice Water containing 10 grams sodium sulfite. The resulting mixture is stirred at 0-10 C. for one hour. The product is collected by filtration and is washed with cold water until neutral and airdried at 25 -30 C. 103 grams of a solid representing a yield of 74% is recovered. The product recrystallized from heptane melts at 69-70 C. Analysis of the product gives nitrogen 9.91% and sulfur 22.72% compared with 9.99% N and 22.87% S calculated for C H N S Example 2 N vtert. butyl N cyclohexyl 2 benzothiazolesulfenamide is prepared in a similar manner except one mole of N tert. butylcyclohexylamine is used in place of N-tertlsutyl-N-isopropyl amine. grams (73% yield) of a solid are recovered; recrystallized from heptane the product melts at 93-94 C. Analysis gives 8.79% N and 19.82% S compared to 8.74% N and 20.00% S calculated for C17H24N2S2.

(Example 3 N-tert.-butyl-N-cyclohexyl 5 chloro-2-benzothiaz olesulfenamide is prepared by the procedure of Example 2 except 5-chloro-Z-mercaptobenzothiazole is used in place of the mercapto'benzothiazole. 6 6 grams (75% yield) of the sulfenamide are recovered. The product recrystallized from ethyl acetate melts at 1'65l'66 C. Analysis gives 7. 88% N and 18.02% S compared to 7.89% N and the new accelerators. The effect on processing safety of substituents in the benzothiazole portion of the molecule is demonstrated.

180778 1 ltdf news TABLEH ca cu a e or 0 1': 2a 2 2 5 stock V V V I J K Example 4 Masterbatch 166.0 166.0 166.0 gulr nr n 1. 1 1.75 1. 7

1 n 0 9X N-tert.-butyl N cyczilohexyl-6-ethoxy-Z-benzothrazolebit -tgbutyl.N.cyclohexylbenzothiazolesulfen- 0 5 sulfenamide is prepare in a like manner by using 6- 10 81111 e ethoxy-2-mercaptobenzofihiazolegrams y 2022151133 155.5352???l ifi i f ffiifififi 0.5 of a solid which melts at -l06-107 C. after recrystalliza- 32 11 Bethox benlflthla- 0 5 tion from alcohol is obtained. Analysis of the product Mooney Scorch at O :j"'f""2ji' 2 13 gives 7.52% N and 17.59% S compared to 7. 68% N and 17597; 3 calculated for C19H28N2OS2' As further examples of the processing safety of the p? compounds can be used accelrators the compounds of the invention, vulcanizable compositions vulcanization of natural and synthetic sulfur-vulcamzable are compounded comprising the following Stocks; rubbers. The special properties of the new delayed-action sulfenamides in rubber stocks compounded in styrene bu- MASTERBATCH tadiene rubber and in blends of styrene butadiene rubber 20 I di P t with polybutadiene rubber are shown below. Oil extended SBR 137.5 The amount of accelerator u'sed depends on a number Carbon black (ISAF) 5.0 of factors uch as process conditions, type of elastomer, Stearic acid 1.0 use of the vulcanized product, other components in the Zinc oxide 3.0 recipe and other variable to which the compounder must Hydrocarbon softener 1.5 address himself. The amount is, however, usually within the range of 0.1 to 5 parts by weight, and more often T t l 208,0 within the range of 0.3 to 2 parts by weight per .100 parts by weight of rubber. The preferred usage generally falls TABLE III within the range of 0.5 and 1.5 parts by weight Stock L M N accelerator- Masterbatch 208. 0 208. 0

A styrene-butadlene masterbatch is used to test the Sulfur.

1.8 1.8 accelerating activity of the new compounds. The masterfig? 1 5?;$1,155,155.55;gggggg gg ggggggg 53g ff batch is prepared by milling the following ingredients: N: 22 y p py 1 2 m N-t *t-but l-N-c clohex l-z benzotha ole- MASTERBATCH Britannia? -i If 1.2 Mooney scorch at 135 0. (t5) 36. 0 42. 5 44. 5 Parts by weight Styrene-butadiene rubber 100.0 MASTERBATCH Carbon B1301; 52.2 lng gdients; Parts Stearic acid 2.0 Styrene-butadiene rubber 68.75 Zinc Oxide "A 4A) Cis-4-polybutadiene rubber 50.0 Hydrocarbon softener 10.0 Carb9n ck (HAP) Steanc acid 2.0 Zinc oxide 3.0 .Total parts 168.0

I Total 183.75 Vulcamzable stocks are prepared by incoroporatmg the accelerator, sulfur, and an antidegradant into the master- TABLE IV batch. The antidegradants used are Santoflex 13 which is Stocks 0 P Q R S .N(l,3-dimethylbutyl)N' phenyl p phenylenediamine Mast b t 1 183 3 1 and Santofiex 77 which is N,N-bis('1,4-dimethyl pentyl)- f I 11;? 11 12 ig? p-phenlenediamine. Curing characteristics are determined gg i 1% 3.0 by means of the Monsanto Oscillating Disk Rheometer i fg iffiggg ff Lo described by Decker, Wise and Guerry in Rubber World, g g i fgg if 1 0 December 1962, page 68. From the Rheometer data the f;;f{ ;f.%3%;. maximum torque is recorded in Rheorneter units. Mooney gg fgfi f gg q H scorch times are determined by means of a Mooney Plasg il g ig fi im iife... tometer. The time in minutes required for the Mooney viscosity to rise five points above the minimum giiffiggffifififiigiliiif viscosity is recorded. Longer times are indicative of fenamide greater processing safety. Mooney scorch at 0. (t 30.7 34.6 35.4 48.4 34. 0

TABLE I Stock A 13 o D E F H Masterbat-ch 168.0 168.0 168.0 168.0 168.0 168.0 168.0 Sulfur 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Santofiex 13... 2.0 2.0 2.0 Santoflex 77 2.0 ..0 .0 2. 0 N-tertbutyl-N-isopropyl-2rbenzothiaz0le sulfenamide 0. 5 1.0 0. 5 1. 0 N -tert-butyl-N-eyc10hexyl-2-benz othiazole sulienamide 0.5 1.0 0.5 1.0 Mooney scorch at 135 C. (1:5) 32.3 28.0 32.4 30. 7 25.9 22.0 27. 1 23.0 Bheometer at 153 0. maximum torpue 66. 0 70.0 63. 0 67.0 62.0 67. 0 60.5 65.8

A similar masterbatch, except that it contains two parts less carbon black, is used to prepare stocks containing MASTERBATCH Ingredients: Parts Natural rubber 100.0 Carbon black (HAF) 45.0 Stearic acid 2.0 Zinc oxide 3.0 Hydrocarbon softener 5.0

Total 155.0

TABLE V 5. 155.0 2. 0 2. 0 Santoflex 13 2. 2. 0 2. 0 N,N-diisopr0py1-2-beuzothiazolesultenamide. 0. 6 Ntert-butyl-N-isopropyl-2-benzothiazolesu1- fenamide 0.6 N tert-butyl-N cyclohexyl-Z-benzothiazolesult'enamide 0.6 Mooney scorch at 121 0. (t 31.6 34. 6 86. 5

The data show that the unsymmetrical dialkyl sulfenamides have considerably more processing safety than the symmetrical dialkyl sulfenamide control. In certain ap plications, an immediate economical advantage is accomplished because the need to add prevulcanization inhibitors is eliminated. The data indicate that substituents on the benzothiazolyl portion of the molecule do not adversely effect the scorch advantage achieved by the unsymmetrical sulfenamides.

Although the invention has been illustrated by typical examples, it is not limited thereto. Changes and modifications of the examples of the invention herein chosen for purposes of disclosure can be made which do not constitute departure from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A compound of the formula wherein T is benzothiazolyl or substituted benzothiazolyl, where the substituents are chloro, bromo, fiuoro, iodo, nitro or ethoxy, R is tertiary-alkyl of 4-12 carbon atoms, R and R are alkyl of 1-8 carbon atoms or together with the carbon atom to which they are attached form cycloalkyl of 5-8 carbon atoms.

2. A compound according to claim 1 wherein T is benzothiazolyl, R is tertiary-butyl and R and R are methyl.

R2 oH 3 is cyclohexyl.

5. A compound according to claim 1 wherein T is 6-ethoxybenzothiazolyl, R is tertiary-butyl and R2 OH is cyclohexyl.

References Cited UNITED STATES PATENTS 3,161,648 12/1964 Rodgers et al. 260306.6

ALEX MAZEL, Primary Examiner R. J. GALLAGHER, Assistant Examiner US. Cl. X.R. 260788 

